This invention relates to convection ovens and more particularly to a gas burner for a fan-driven convection apparatus.
Convection ovens are well known in the art. They are heated, in a convection mode by both electrical heaters and by gas-fired burners. Generally, where gas-fired burners are used, the heating operation is done in one of two ways. Either the burner is located in a separate chamber from the fan, buffered from its turbulence, or an indirect heat exchanger is interposed between the gas burner and the fan. Disclosures of several electrical heating element ovens suggest that a gas burner could be used in place of the electric heating element, but none of these prior disclosures show how this can be done.
More particularly, the use of a gas burner in a convection oven is problematic and generally requires either a separate, buffered burner chamber or an interposed heat exchanger. This is due to the problem of sustaining adequate flame configuration in the presence of the turbulent air flow in the same chamber or area as the fan. The fan flow turbulence has a tendency to separate the flame from its anchoring burner and to extinguish the flame, severely incapacitating the efficiency of the burner. Also, the flame must be lit or initiated when the burner is turned on. Turbulent air flow in the fan chamber affects the ignition operation and hampers flame ignition, blowing the gas away from the ignitor.
Moreover, electric heating elements in convection ovens have several disadvantages. First, since the element heats around its entire surface area, it also radiates heat onto the back surfaces of the oven structure so that some of the heat radiated is wasted and does not reach the cooking chamber. Secondly, such convection ovens are generally preheated using a broiler burner. Once the preheat reaches a certain level, the broiler element is turned off and the convection element is turned on. There is a lag in the electric convection element from the time it is turned on to the time it reaches its appropriate operating temperature. Therefore, the preheat temperature in the oven drops off, and some of the preheat energy is lost.
Accordingly, it has been one objective of this invention to provide an improved convection oven with an operable, efficient gas burner disposed in the same area as the convection fan.
Another objective of the invention has been to provide an improved gas burner for a convection oven.
To these ends a gas, convection burner according to one embodiment of the invention overcomes these difficulties and provides an effective gas burner for use in a convection oven. This is accomplished by several factors. First, the burner is formed of a tube having a circular, rectangular, or square cross-section and preferably bent in a circular configuration. Preferably two inlet ends of the tube are interconnected to a fitting, which itself is connected to a gas source.
A series of slots are located in preferably the outer periphery or face of the tube. Each of these slots is 0.1875 to one inch long and approximately 0.018xe2x80x3 to 0.023xe2x80x3 wide. The circular cross-section tube is about one-half to three-quarters inch in diameter with 0.035 inches wall thickness, and forms a circular shape of about 7.25 inches outside diameter. Tubing of other cross-sectional shapes may be of similar or equivalent dimensions as desired. The burner configuration produces a short, tight and stable flame with the gas pressure at each of the slots from the respective tube inputs remaining relatively consistent. It has been found that when a burner of this configuration is utilized in a convection oven environment, together with a fan for blowing heated air into a convection cooking chamber; even the turbulent flow of the fan does not blow out the flames.
Preferably, the burner is disposed around the outer periphery of a convection fan. A short, cylindrical sleeve extends along the fan axis between the fan outer periphery and the burner, and serves as an inner burner baffle. A flat ring extends radially from proximate the downstream end of the cylindrical sleeve, with respect to air flow through the fan, at least coextensively with and preferably outwardly of the outer periphery of the annular burner and near one side of the annular burner. This ring serves as an outer burner baffle.
A direct spark ignitor or HSI (hot surface igniter), as well known in the industry, is utilized. Once the igniter gets a start signal, it begins to spark or glow, until a flame rectification rod indicates the presence of a flame on the burner. If that does not occur within a preset time duration of, say, six seconds or so, the voltage to the gas valve is dropped off and the gas valve closes for safety reasons.
Such a gas burner, when used in a convection oven, produces several advantages. For example, since the flame is in or proximate the fan path, and in the same chamber as the fan, most of the heat generated by the burner is directed by the air flow into the chamber and is not wasted radiating in other directions. Secondly, the burner reaches operating temperature much more quickly than does an electric element, reducing preheat energy loss. Accordingly, when used in a convection oven, once a preheat temperature is obtained and the burner turned on, there is much less lag in the desired rise in operating temperature and less heat is lost in the interim. Also, the burner can produce the same temperature gradients as an electric burner so that the processes remain similar in terms of the time and temperature settings for predetermined foods.
Perhaps most importantly, however, the burner described produces a tight flame, not susceptible to being blown out by the convention fan mounted in the same chamber and which can also be ignited despite the ongoing fan flow.
Accordingly, a gas convection burner is provided which can be effectively and efficiently used in a convection oven. The gas burner has the advantage of producing a uniform heat in a shorter duration of time from start up than an electrical element, since its gradient from start to operating temperature is much quicker than a typical electrical burner. At the same time, it provides a heating gradient for a normal heating process similar to the electric heating element, and it does not suffer from flame blow-out or ignition interference even though disposed in the fan turbulence as a gas burner may be expected to do.
It will be appreciated that the gas burner as disclosed herein can be used effectively in many types of convection ovens, both commercial and residential, and has also applications in ranges and ovens for either commercial or residential use.
These and other objectives and advantages will become readily apparent from the following detailed description of a preferred embodiment of the invention and from the drawings in which: